Head-mounted display apparatus

ABSTRACT

A head-mounted display apparatus includes an image display device, a wearing device with which the image display device is worn on a head of an observer, and an attachment member with which the image display device is attached to the wearing device. The attachment member is capable of adjusting a position of the image display device relative to the wearing device independently in a first direction and in a second direction, the first direction being defined by a virtual line connecting centers of eyes of the observer, the second direction being perpendicular to the first direction and extending vertically with respect to the observer.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/604,800, filed on Oct. 23, 2009, which claims priority to JapanesePriority Patent Application JP 2008-272879 filed in the Japan PatentOffice on Oct. 23, 2008, the entire content of which is herebyincorporated by reference.

BACKGROUND

The present application relates to head-mounted display apparatuses tobe worn on heads of observers.

There are some virtual-image display devices (image display devices)each enabling an observer to observe a two-dimensional image formed byan image-forming device in a form of a virtual image enlarged by avirtual-image optical system, as disclosed in, for example, JapaneseUnexamined Patent Application Publication No. 2006-162767.

FIG. 8 is a conceptual diagram of an exemplary image display device 100.The image display device 100 includes an image-forming device 111 havinga plurality of pixels arranged in a two-dimensional matrix, acollimating optical system 112 collimating light emitted from the pixelsof the image-forming device 111 into parallel light, and an opticaldevice (light-guiding means) 120 receiving the parallel light from thecollimating optical system 112, guiding the light therethrough, andoutputting the light. The image-forming device 111 and the collimatingoptical system 112 constitute an image generator 110. The optical device120 includes a light-guiding plate 121 causing the received light topropagate with total reflection thereinside before outputting the light,first deflecting means 130 (for example, a layer of light-reflectingfilm) reflecting the light received by the light-guiding plate 121 sothat the light is totally reflected inside the light-guiding plate 121,and second deflecting means 140 (for example, a multilayer structure inwhich a number of light-reflecting films are stacked) causing the lightthat has propagated with total reflection inside the light-guiding plate121 to be output from the light-guiding plate 121.

There are other virtual-image display devices (image display devices)each employing hologram diffraction gratings so that an observer canobserve a two-dimensional image formed by an image-forming device in theform of a virtual image enlarged by a virtual-image optical system, asdisclosed in, for example, Japanese Unexamined Patent ApplicationPublication No. 2007-94175.

FIG. 10A is a conceptual diagram of an exemplary image display device300. The image display device 300 basically includes the image-formingdevice 111 displaying an image, the collimating optical system 112, andan optical device (light-guiding means) 320 receiving light of the imagedisplayed on the image-forming device 111 and guiding the lighttherethrough toward an eye 41 of an observer. The optical device 320includes a light-guiding plate 321, and first and second diffractiongrating members 330 and 340 provided on the light-guiding plate 321. Thediffraction grating members 330 and 340 are reflective volume-hologramdiffraction gratings. The collimating optical system 112 receives lightemitted from the pixels of the image-forming device 111, collimates thelight into parallel light, and outputs the parallel light toward thelight-guiding plate 321. The parallel light enters and is output from afirst surface 322 of the light-guiding plate 321. The first and seconddiffraction grating members 330 and 340 are provided on a second surface323 of the light-guiding plate 321, the second surface 323 beingparallel to the first surface 322.

In a head-mounted display (HMD) apparatus in which two image displaydevices are to be worn on the head of an observer, it is important thatthe distance between the two image display devices matches the distancebetween the eyes of the observer. The distance between the centers ofthe eyes varies between individuals, ranging from about 58 mm to about72 mm, within a difference of about 14 mm. Accordingly, each of the twoimage display devices is desirably movable by about 7 mm in a firstdirection, which is a direction defined by a virtual line connecting thecenters of the eyes of the observer. A direction perpendicular to thefirst direction, or a vertical direction with respect to the observer,is defined as a second direction.

Examples of such a binocular head-mounted image display apparatusincluding a mechanism configured to adjust the distance between rightand left image display devices are disclosed in, for example, JapaneseUnexamined Patent Application Publications No. 8-136853 and No. 8-136858

SUMMARY

The mechanisms each configured to adjust the distance between right andleft image display devices disclosed in Japanese Unexamined PatentApplication Publications No. 8-136853 and No. 8-136858 have complexconfigurations and are therefore not practical in size and weightreduction. Moreover, adjustment of the right and left image displaydevices in the second direction is performed as adjustment of theheights of the nose pads. It is difficult to simplify the structures ofthe nose pads. Particularly, it is difficult to reduce the number ofcomponents to be positioned in front of the observer's face.

It is desirable that the present invention provide a head-mounteddisplay apparatus including image display devices each having a simpleadjustment mechanism so that the head-mounted display apparatus can beappropriately worn by an observer.

According to an embodiment, a head-mounted display apparatus includesthe following:

(A) an image display device;

(B) a wearing device with which the image display device is worn on ahead of an observer; and

(C) an attachment member with which the image display device is attachedto the wearing device.

The attachment member is capable of adjusting a position of the imagedisplay device relative to the wearing device independently in a firstdirection and in a second direction, the first direction being definedby a virtual line connecting centers of eyes of the observer, the seconddirection being perpendicular to the first direction and extendingvertically with respect to the observer.

The head-mounted display apparatus according to an embodiment includesthe attachment member with which the image display device is attached tothe wearing device. The attachment member is capable of freely adjustingthe position of the image display device relative to the wearing deviceindependently in the first and second directions, or in the vertical andhorizontal directions relative to the eye of the observer. Thus, theoverall configuration of the head-mounted display apparatus can besimplified, and the number of components to be positioned in front ofthe face of the observer can be reduced easily. The apparatus isparticularly suitable for application as a head-mounted displayapparatus including an image display device whose pupil diameter is 10mm or smaller.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a head-mounted display apparatusaccording to a first exemplary embodiment;

FIG. 2 is a perspective view of the head-mounted display apparatus ofthe first exemplary embodiment, with some components removed;

FIG. 3 is a perspective view of an attachment member, in an assembledstate, included in the head-mounted display apparatus of the firstexemplary embodiment;

FIG. 4 is a side view of the attachment member, in the assembled state,included in the head-mounted display apparatus of the first exemplaryembodiment;

FIG. 5 is an exploded perspective view of the attachment member includedin the head-mounted display apparatus of the first exemplary embodiment;

FIG. 6 is another exploded perspective view of the attachment memberincluded in the head-mounted display apparatus of the first exemplaryembodiment, seen in a different direction from FIG. 5;

FIG. 7A is a schematic cross-sectional view of a part of the attachmentmember, including a support member and a retaining member havinggrooves, and FIGS. 7B and 7C are schematic cross-sectional views ofrelevant parts including the support member, the grooves, depressions,balls, guide member, and the retaining member showing the arrangementthereof;

FIG. 8 is a conceptual diagram of an image display device included inthe head-mounted display apparatus of the first exemplary embodiment;

FIG. 9 is a conceptual diagram of an image display device included in ahead-mounted display apparatus according to a second exemplaryembodiment;

FIGS. 10A and 10B are a conceptual diagram of an image display deviceincluded in a head-mounted display apparatus according to a thirdexemplary embodiment, and a schematic enlarged cross-sectional viewshowing a part of a reflective volume-hologram diffraction grating;

FIG. 11 is a conceptual diagram of an image display device included in ahead-mounted display apparatus according to a fourth exemplaryembodiment;

FIG. 12 is a conceptual diagram of an image display device included in ahead-mounted display apparatus according to a fifth exemplaryembodiment;

FIG. 13 is a conceptual diagram of an image-forming device suitable foruse as a variation of each of image-forming devices in the first, third,and fifth exemplary embodiments;

FIG. 14 is a conceptual diagram of an image-forming device suitable foruse as another variation of each of the image-forming devices in thefirst, third, and fifth exemplary embodiments;

FIG. 15 is a conceptual diagram of an image-forming device suitable foruse as yet another variation of each of the image-forming devices in thefirst, third, and fifth exemplary embodiments;

FIG. 16 is a conceptual diagram of an image-forming device suitable foruse as yet another variation of each of the image-forming devices in thefirst, third, and fifth exemplary embodiments; and

FIG. 17 is a conceptual diagram of an image-forming device suitable foruse as yet another variation of each of the image-forming devices in thefirst, third, and fifth exemplary embodiments.

DETAILED DESCRIPTION

The present application will be described below with reference to theaccompanying drawings according to an embodiment. The presentapplication is not limited to the embodiments described below.Descriptions will be given in the following order:

1. Head-mounted display apparatus according to an embodiment.

2. First exemplary embodiment (specific description of a head-mounteddisplay apparatus according to a first exemplary embodiment of thepresent invention including image generators having a firstconfiguration and optical devices having a first configuration)

3. Second exemplary embodiment (specific description of anotherhead-mounted display apparatus, a variation of the first exemplaryembodiment, including image generators having a second configuration andoptical devices having the first configuration)

4. Third exemplary embodiment (specific description of anotherhead-mounted display apparatus, another variation of the first exemplaryembodiment, including image generators having the first configurationand optical devices having a second configuration)

5. Fourth exemplary embodiment (specific description of anotherhead-mounted display apparatus, another variation of the first exemplaryembodiment, including image generators having the second configurationand optical devices having the second configuration)

6. Fifth exemplary embodiment (specific description of anotherhead-mounted display apparatus, another variation of the first exemplaryembodiment, including optical devices having a third configuration)

Head-Mounted Display

In the head-mounted display (HMD) apparatus according to an embodiment,it is preferred that the attachment member include the following:

(C-1) first, second, and third balls;

(C-2) a support member having a first linear groove includingconsecutive depressions, a second linear groove parallel to the firstgroove and including consecutive depressions, and a third linear grooveparallel to the first groove and including consecutive depressions;

(C-3) a retaining member having a fourth linear groove orthogonal to thefirst groove and including consecutive depressions, a fifth lineargroove parallel to the fourth groove and including consecutivedepressions, and a sixth linear groove parallel to the fourth groove andincluding consecutive depressions; and

(C-4) an urging member urging the retaining member against the supportmember.

In a state where the retaining member is urged against the supportmember by the urging member, the first ball fits into the first andfourth grooves, the second ball fits into the second and fifth grooves,and the third ball fits into the third and sixth grooves, with the firstto third balls being positioned at respective apexes of a virtualtriangle. The image display device is attached to the support member.The wearing device is attached to the retaining member.

The first to third grooves may extend in the first direction, with thefourth to sixth grooves extending in the second direction.Alternatively, the first to third grooves may extend in the seconddirection, with the fourth to sixth grooves extending in the firstdirection. Furthermore, the virtual triangle may be of any shape, forexample, an equilateral triangle or an isosceles triangle. The first tosixth grooves may be of any lengths larger than the range within whichthe image display device is to be moved.

In this case, a guide member may be provided between the support memberand the retaining member, the guide member having receiving portionsthat receive the first to third balls, respectively, so as to positionthe first to third balls at the apexes of the virtual triangle.

The first to third balls may be, for example, steel balls for use asball bearings. The support member, the retaining member, the urgingmember, and the guide member may be made of any of materials includingplastics such as polyoxymethylene (POM) resin, acrylonitrile butadienestyrene (ABS) resin, poly(phenylene sulfide) (PPS) resin, andpolycarbonate (PC) resin, metals such as stainless steel, titanium,aluminum, and brass, and alloys thereof, by appropriate methods. Theimage display device and the wearing device may be attached to thesupport member and the retaining member, respectively, with screws orthe like.

In the above preferred embodiment including the above preferredconfiguration, the first and fourth grooves may be spot-faced so thatthe first ball is received stably, the second and fifth grooves may bespot-faced so that the second ball is received stably, and the third andsixth grooves may be spot-faced so that the third ball is receivedstably.

In the head-mounted display apparatus according to the above preferredembodiment including the above preferred configuration, the imagedisplay device and the attachment member may be provided for each of theright and left eyes. Alternatively, the image display device and theattachment member may be provided for one of the right and left eyes.

In the head-mounted display apparatus according to the above preferredembodiment including the above preferred configuration, the imagedisplay device may include the following:

(A-1) an image generator; and

(A-2) an optical device (light-guiding means) receiving light from theimage generator, guiding the light, and outputting the light toward acorresponding one of the eyes of the observer.

The optical device may be attached to the image generator, for example.

The optical device (light-guiding means) may include the following:

(A-2-1) a light-guiding plate causing the received light to propagatewith total reflection thereinside before outputting the light;

(A-2-2) a first deflector deflecting the light received by thelight-guiding plate so that the light is totally reflected inside thelight-guiding plate; and

(A-2-3) a second deflector deflecting, a plurality of times, the lightcaused to propagate with total reflection inside the light-guiding plateso that the light is output from the light-guiding plate.

The term “total reflection” means internal total reflection or totalreflection inside the light-guiding plate. This also applies to thedescription hereinafter.

In the optical device according to such an embodiment, the firstdeflector may reflect the light received by the light-guiding plate, andthe second deflector may transmit and reflect, a plurality of times, thelight caused to propagate with total reflection inside the light-guidingplate. For convenience of description hereinafter, an optical devicehaving such a configuration will be referred to as an “optical devicehaving the first configuration”. In this case, the first deflector mayfunction as a reflective mirror, and the second deflector may functionas a transflective mirror.

In such a configuration, the first deflector may be made of metal,inclusive of alloy, for example, and may be a light-reflecting film (akind of a mirror) that reflects the light received by the light-guidingplate, or a diffraction grating (for example, a hologram diffractiongrating film) that diffracts the light received by the light-guidingplate. The second deflector may be any of the following: a multilayerstructure in which a number of dielectric films are stacked, a halfmirror, a polarization beam splitter, and a hologram diffraction gratingfilm. The first and second deflectors are provided inside (orincorporated in) the light-guiding plate. The first deflector reflectsor diffracts the parallel light received by the light-guiding plate sothat the parallel light is totally reflected inside the light-guidingplate. The second deflector reflects or diffracts, a plurality of times,the parallel light caused to propagate with total reflection inside thelight-guiding plate, and outputs the light, maintaining the form ofparallel light, from the light-guiding plate.

In the optical device according to such an embodiment, the firstdeflector may diffract the light received by the light-guiding plate,and the second deflector may diffract, a plurality of times, the lightcaused to propagate with total reflection inside the light-guidingplate. For convenience of description hereinafter, an optical devicehaving such a configuration will be referred to as an “optical devicehaving the second configuration”. In this case, the first and seconddeflectors may include diffraction grating elements. The diffractiongrating elements may be reflective diffraction grating elements ortransmissive diffraction grating elements. As another alternative, oneof the diffraction grating elements may be a reflective diffractiongrating element and the other may be a transmissive diffraction gratingelement. Examples of the reflective diffraction grating elements includereflective volume-hologram diffraction gratings. For convenience ofdescription hereinafter, a first deflector constituted by a reflectivevolume-hologram diffraction grating will be occasionally referred to asa “first diffraction grating member”, and a second deflector constitutedby a reflective volume-hologram diffraction grating will be occasionallyreferred to as a “second diffraction grating member”.

To accommodate diffraction reflections of a number P (specifically, P=3,corresponding to three colors of red, green, and blue) of kinds of lighthaving a number P of different spectrum bands (or wavelengths), thefirst and second diffraction grating members may each include a number Pof diffraction grating layers, as reflective volume-hologram diffractiongratings, that are stacked one on top of another. Each of thediffraction grating layers has a pattern of interference fringescorresponding to one of the spectrum bands (or wavelengths).Alternatively, to accommodate diffraction reflections of a number P ofkinds of light having a number P of different spectrum bands (orwavelengths), the first and second diffraction grating members may eachinclude a single diffraction grating layer having a number P of kinds ofinterference-fringe patterns. In another alternative case, the first andsecond diffraction grating members may each include a stack ofdiffraction grating layers provided in correspondence with, for example,three equally divided angles of view. With any of such configurations,light of the different spectrum bands (or wavelengths) can be diffractedand reflected by the first and second diffraction grating members withan increased diffraction efficiency, a widened diffraction acceptanceangle, and an optimized diffraction angle.

Examples of materials composing the first and second diffraction gratingmembers include photopolymer materials. The materials and basicconfigurations of the first and second diffraction grating members, asreflective volume-hologram diffraction gratings, may be the same asthose of related-art reflective volume-hologram diffraction gratings.Herein, a reflective volume-hologram diffraction grating means ahologram diffraction grating that diffracts and reflects light so as toonly produce +1st-order diffracted light. The foregoing diffractiongrating members each have interference fringes extending thereinside,from one surface thereof to the other. The interference fringes may beformed by a related-art method. Specifically, the interference fringesmay be formed as follows. Object light is applied, in a first direction,to one side of a member (for example, a photopolymer material) that isto become the diffraction grating member. At the same time, referencelight is applied to the other side of the member in a second direction.The object light and the reference light produce interference fringes.These interference fringes are recorded inside the member. Byappropriately setting the first and second directions and thewavelengths of the object light and the reference light, theinterference fringes can be formed at a desired pitch on the surface ofthe diffraction grating member and at a desired slant angle. Herein, theslant angle of interference fringes means an angle formed between thesurface of the diffraction grating member (or the diffraction gratinglayer) and each of the interference fringes. In a case where the firstand second diffraction grating members each have a multilayer structureincluding a number P of diffraction grating layers as reflectivevolume-hologram diffraction gratings, a stack of the diffraction gratinglayers may be obtained by making the number P of diffraction gratinglayers separately and subsequently stacking (bonding) the diffractiongrating layers with ultraviolet-curable adhesive or the like providedtherebetween. Alternatively, the number P of diffraction grating layersmay be obtained by preparing a diffraction grating layer made of acohesive photopolymer material, and then sequentially providing otherlayers of cohesive photopolymer material thereon.

In the head-mounted display apparatus according to an embodiment, theoptical device may alternatively include a transflective mirrorreceiving the light from the image generator and outputting the lighttoward the eye of the observer. For convenience of descriptionhereinafter, an optical device having such a configuration will bereferred to as an “optical device having the third configuration”. Lightemitted from the image generator may propagate either in the air orinside a transparent member such as a glass plate or a plastic plate(specifically, a member made of the same material as of thelight-guiding plate described below) before entering the transflectivemirror. Depending on circumstances, the transflective mirror may beattached to the image generator with either the transparent member oranother different member interposed therebetween.

In the head-mounted display apparatus according to an above preferredembodiment including the above preferred configuration, the imagegenerator may include the following:

(A-1-1) an image-forming device having a plurality of pixels arranged ina two-dimensional matrix; and

(A-1-2) a collimating optical system collimating light from the pixelsof the image-forming device into parallel light and outputting theparallel light.

For convenience of description hereinafter, an image generator havingsuch a configuration will be referred to as an “image generator havingthe first configuration”.

The image-forming device included in the image generator having thefirst configuration may be any of the following: an image-forming deviceincluding a reflective spatial-light modulator and a light source, animage-forming device including a transmissive spatial-light modulatorand a light source, and an image-forming device including light-emittingelements such as organic electroluminescent (EL) elements, inorganic ELelements, light-emitting diodes (LEDs), or the like. In particular, theimage-forming device including a reflective spatial-light modulator anda light source is preferable. Examples of the spatial-light modulatorinclude a light valve such as a transmissive or reflective liquidcrystal display device such as a liquid-crystal-on-silicon (LCOS)device, and a digital micromirror device (DMD). Examples of the lightsource include a light-emitting element. The reflective spatial-lightmodulator may include a liquid crystal display device and a polarizationbeam splitter that reflects part of light from the light source andguides the part of light to the liquid crystal display device whileallowing part of light reflected by the liquid crystal display device topass therethrough and guiding the part of light to the collimatingoptical system. Examples of the light-emitting element constituting thelight source include a red-light-emitting element, agreen-light-emitting element, a blue-light-emitting element, and awhite-light-emitting element. Such light-emitting elements may be, forexample, semiconductor light-emitting elements such as semiconductorlaser elements or LEDs. The number of pixels may be determined inaccordance with desired specifications of the head-mounted displayapparatus. For example, the number of pixels may be 320×240, 432×240,640×480, 1024×768, or 1920×1080.

In the head-mounted display apparatus according to the above preferredembodiment including the above preferred configuration, the imagegenerator may include the following:

(A-1-1) a light source;

(A-1-2) a collimating optical system collimating light from the lightsource into parallel light;

(A-1-3) a scanner scanningly moving the parallel light from thecollimating optical system; and

(A-1-4) a relay optical system relaying and outputting the parallellight scanningly moved by the scanner.

For convenience of description hereinafter, an image generator havingsuch a configuration will be referred to as an “image generator havingthe second configuration”.

Examples of the light source included in the image generator having thesecond configuration include a light-emitting element, such as ared-light-emitting element, a green-light-emitting element, ablue-light-emitting element, and a white-light-emitting element. Suchlight-emitting elements may be, for example, semiconductorlight-emitting elements such as semiconductor laser elements or LEDs.The number of pixels (virtual pixels) included in the image generatorhaving the second configuration may also be determined in accordancewith desired specifications of the head-mounted display apparatus. Forexample, the number of pixels (virtual pixels) may be 320×240, 432×240,640×480, 1024×768, or 1920×1080. In a case where the light sourceincludes red-, green-, and blue-light-emitting elements, it is preferredthat the colors of the light be combined by using, for example, a crossprism. Examples of the scanner include a microelectromechanical system(MEMS) including a micromirror rotatable in two-dimensional directions,and a galvanometer mirror. The MEMS and the galvanometer mirrorscanningly move the light from the light source in the horizontal andvertical directions. The relay optical system may be configured as inthe related art.

An example of the image-forming device or the light source constitutedby a light-emitting element and a light valve is a combination of abacklight that emits white light on the whole and a liquid crystaldisplay device having red-, green-, and blue-light-emitting elements.Other exemplary configurations will now be described below.

Image-Forming Device A

An image-forming device A includes the following:

(α) a first image-forming unit including a first light-emitting panel onwhich first light-emitting elements that emit blue light are arranged ina two-dimensional matrix;

(β) a second image-forming unit including a second light-emitting panelon which second light-emitting elements that emit green light arearranged in a two-dimensional matrix;

(γ) a third image-forming unit including a third light-emitting panel onwhich third light-emitting elements that emit red light are arranged ina two-dimensional matrix; and

(δ) means (a dichroic prism, for example; the same applies to otherimage-forming devices described below) for combining the light emittedfrom the first, second, and third image-forming units into a single rayof light.

The image-forming device A controls the first to third light-emittingelements to individually switch between emitting and non-emittingstates.

Image-Forming Device B

An image-forming device B includes the following:

(α) a first image-forming unit including a first light-emitting elementthat emits blue light and a first light-passage control device (a kindof a light valve such as a liquid crystal display device, a DMD, or anLCOS; the same applies to the description hereinafter) that controls thelight emitted from the first light-emitting element to pass therethroughor to be blocked thereby;

(β) a second image-forming unit including a second light-emittingelement that emits green light and a second light-passage control device(a light valve) that controls the light emitted from the secondlight-emitting element to pass therethrough or to be blocked thereby;

(γ) a third image-forming unit including a third light-emitting elementthat emits red light and a third light-passage control device (a lightvalve) that controls the light emitted from the third light-emittingelement to pass therethrough or to be blocked thereby; and

(δ) means for combining the light that has passed through the first tothird light-passage control devices into a single ray of light.

The image forming device B displays an image by controlling with thelight-passage control devices the passage/blockage of the light emittedfrom the respective light-emitting elements. Examples of means(light-guiding members) for guiding the light emitted from the first tothird light-emitting elements to the respective light-passage controldevices include microlens arrays, mirrors, reflective plates, andcondenser lenses.

Image-Forming Device C

An image-forming device C includes the following:

(α) a first image-forming unit including a first light-emitting panel onwhich first light-emitting elements that emit blue light are arranged ina two-dimensional matrix, and a blue-light-passage control device (alight valve) that controls the light emitted from the firstlight-emitting panel to pass therethrough or to be blocked thereby;

(β) a second image-forming unit including a second light-emitting panelon which second light-emitting elements that emit green light arearranged in a two-dimensional matrix, and a green-light-passage controldevice (a light valve) that controls the light emitted from the secondlight-emitting panel to pass therethrough or to be blocked thereby;

(γ) a third image-forming unit including a third light-emitting panel onwhich third light-emitting elements that emit red light are arranged ina two-dimensional matrix, and a red-light-passage control device (alight valve) that controls the light emitted from the thirdlight-emitting panel to pass therethrough or to be blocked thereby; and

(δ) means for combining the light that has passed through the blue-,green-, and red-light-passage control devices into a single ray oflight.

The image-forming device C displays an image by controlling with thelight-passage control devices (light valves) the passage/blockage of thelight emitted from the respective light-emitting panels.

Image-Forming Device D

An image forming device D is a field-sequential color image-formingdevice and includes the following:

(α) a first image-forming unit having a first light-emitting elementthat emits blue light;

(β) a second image-forming unit having a second light-emitting elementthat emits green light;

(γ) a third image-forming unit having a third light-emitting elementthat emits red light;

(δ) means for combining the light emitted from the first to thirdimage-forming units into a single ray of light; and

(∈) a light-passage control device (a light valve) that controls thelight emitted from the means for combining the light to passtherethrough or to be blocked thereby.

The image-forming device D displays an image by controlling with thelight-passage control device the passage/blockage of the light emittedfrom the light-emitting elements.

Image-Forming Device E

An image forming device E is also a field-sequential color image-formingdevice and includes the following:

(α) a first image-forming unit including a first light-emitting panel onwhich first light-emitting elements that emit blue light are arranged ina two-dimensional matrix;

(β) a second image-forming unit including a second light-emitting panelon which second light-emitting elements that emit green light arearranged in a two-dimensional matrix;

(γ) a third image-forming unit including a third light-emitting panel onwhich third light-emitting elements that emit red light are arranged ina two-dimensional matrix;

(δ) means for combining the light emitted from the first to third imageforming units into a single ray of light; and

(∈) a light-passage control device (a light valve) that controls thelight emitted from the means for combining the light to passtherethrough or to be blocked thereby.

The image forming device E displays an image by controlling with thelight-passage control device the passage/blockage of the light emittedfrom the first to third light-emitting panels.

Image-Forming Device F

An image forming device F is a passive-matrix or active-matrix colorimage-forming device, and displays an image by controlling first, secondand third light-emitting elements to individually switch betweenemitting and non-emitting states.

Image-Forming Device G

An image forming device G is a field-sequential color image-formingdevice and includes a light-passage control device (a light valve) thatcontrols light emitted from light-emitting-element units arranged in atwo-dimensional matrix to pass therethrough or to be blocked thereby.The image forming device G displays an image by controlling, in atime-shared manner, first, second, and third light-emitting elementsincluded in the light-emitting-element units to individually switchbetween emitting and non-emitting states, and by controlling with thelight-passage control device the passage/blockage of the light emittedfrom the first to third light-emitting elements.

In each of the image generators having the first and secondconfigurations, light is collimated by the collimating optical systeminto a plurality of parallel rays, and the parallel rays are caused toenter the light-guiding plate. The reason for producing parallel rays isbecause optical wavefront information obtained when the light enters thelight-guiding plate is to be maintained in the same form even after thelight strikes the first and second deflectors and is output from thelight-guiding plate. To produce a plurality of parallel rays, theimage-forming device may be positioned at a distance from thecollimating optical system corresponding to the focal length of thecollimating optical system, for example. The collimating optical systemhas a function of converting positional information on pixels intoangular information in the optical system of the optical device. Thecollimating optical system may be any of or any combination of a convexlens, a concave lens, a free-form-surface prism, and a hologram lens aslong as the collimating optical system can have a positive optical poweron the whole.

The light-guiding plate has two parallel surfaces (a first surface and asecond surface) extending in the axial direction (Y direction) thereof.The surface of the light-guiding plate from which light enters isdefined as the plane of incidence, and the surface of the light-guidingplate from which light emerges is defined as the plane of emergence. Thefirst surface may serve as both the plane of incidence and the plane ofemergence. Alternatively, the first surface and the second surface mayserve as the plane of incidence and the plane of emergence,respectively. Examples of the material composing the light-guiding plateinclude glasses such as quartz glass and optical glasses including BK7,and plastic materials such as poly(methylmethacrylate) (PMMA),polycarbonate resin, acrylic resin, noncrystalline polypropylenic resin,stylenic resin including acrylonitrile-styrene (AS) resin. Thelight-guiding plate is not limited to a flat plate, and may be a curvedplate.

In the head-mounted display apparatus according to the above preferredembodiment including the above preferred configuration, the wearingdevice may form a frame of a pair of glasses. In addition, the frame mayinclude a front member to be positioned in front of the observer, andtwo temples turnably attached to respective ends of the front memberwith hinges, the attachment member being attached to each of the ends ofthe front member. The front member is provided with a nose pad at thecenter thereof. That is, the frame of the above embodiment hassubstantially the same configuration as a pair of normal glasses, exceptthat the frame includes no rims. The frame may be made of any of or anycombination of materials such as metal, alloy, and plastic, which areused for making normal glasses.

First Exemplary Embodiment

A first exemplary embodiment relates to the head-mounted displayapparatus according to an embodiment. FIGS. 1 and 2 are perspectiveviews of a head-mounted display apparatus according to the firstexemplary embodiment. FIG. 3 is a perspective view of an attachmentmember in an assembled state. FIG. 4 is a side view of the attachmentmember in the assembled state. FIG. 5 is an exploded perspective view ofthe attachment member. FIG. 6 is another exploded perspective view ofthe attachment member seen in a different direction from FIG. 5.

The head-mounted display of the first exemplary embodiment includes thefollowing:

(A) image display devices 100;

(B) a wearing device 20 with which the image display devices 100 areworn on the head of an observer; and

(C) attachment members 30 with which the image display devices 100 areattached to the wearing device 20.

The attachment members 30 are each capable of adjusting the position ofa corresponding one of the image display devices 100 relative to thewearing device 20 independently in a first direction and in a seconddirection. The first direction is defined by a virtual line connectingthe centers of the eyes of the observer. The second direction isperpendicular to the first direction and extends in the verticaldirection with respect to the observer. The head-mounted displayapparatus of the first exemplary embodiment includes two image displaydevices 100 and two attachment members 30 for the right and left eyes.FIG. 1 shows a state where the image display devices 100 are coveredwith covers 113. FIG. 2 shows a state where the image display devices100 are exposed without the covers 113 and lens shields 22 that protectlight-guiding plates 121, which will be described separately below.

Specifically, the attachment members 30 each include the following:

(C-1) first, second, and third balls 33A, 33B, and 33C;

(C-2) a support member 31;

(C-3) a retaining member 35; and

(C-4) urging members 37, 38, and 39 urging the retaining member 35against the support member 31.

The support member 31 has in a surface thereof facing the retainingmember 35 a first linear groove 32A including consecutive depressions, asecond linear groove 32B parallel to the first groove 32A and includingconsecutive depressions, and a third linear groove 32C parallel to thefirst groove 32A and including consecutive depressions. The retainingmember 35 has in a surface thereof facing the support member 31 a fourthlinear groove 36A orthogonal to the first groove 32A and includingconsecutive depressions, a fifth linear groove 36B parallel to thefourth groove 36A and including consecutive depressions, and a sixthlinear groove 36C parallel to the fourth groove 36A and includingconsecutive depressions. In the first exemplary embodiment, the first tothird grooves 32A to 32C extend in the second direction, and the fourthto sixth grooves 36A to 36C extend in the first direction.Alternatively, the first to third grooves 32A to 32C may extend in thefirst direction, with the fourth to sixth grooves 36A to 36C extendingin the second direction. The urging members include an urging plate 37,urging springs 38, and urging screws 39. The support member 31 has onthe surface thereof facing the retaining member 35 three bosses 32D. Theurging screws 39 are screwed into the bosses 32D, respectively.

In a state where the retaining member 35 is urged against the supportmember 31 by the urging members, the first ball 33A fits into the firstand fourth grooves 32A and 36A, the second ball 33B fits into the secondand fifth grooves 32B and 36B, and the third ball 33C fits into thethird and sixth grooves 32C and 36C. In this state, the first to thirdballs 33A to 33C are positioned at the respective apexes of a virtualtriangle (specifically in the first exemplary embodiment, an isoscelestriangle).

The image display devices 100 are attached to the respective supportmembers 31 (specifically, to respective securing members 25 provided onthe wearing device 20) with screws (not shown), and the wearing device20 is attached to the retaining members 35 with screws (not shown).

To position the first to third balls 33A to 33C at the apexes of thevirtual triangle, a guide member 34 is provided between the supportmember 31 and the retaining member 35. The guide member 34 has receivingportions (a kind of through holes) that receive the first to third balls33A to 33C, respectively. The guide member 34 restricts the movements ofthe balls 33A to 33C. FIG. 7B is a schematic cross-sectional view ofrelevant parts including the support member 31, the grooves 32, thedepressions, the balls 33, the guide member 34, and the retaining member35, showing the arrangement thereof.

The first and fourth grooves 32A and 36A are spot-faced so that thefirst ball 33A is received stably. The second and fifth grooves 32B and36B are spot-faced so that the second ball 33B is received stably. Thethird and sixth grooves 32C and 36C are spot-faced so that the thirdball 33C is received stably. Specifically, the grooves 32 each includeconsecutive depressions with elevations interposed therebetween, thedepressions each receiving about ⅓ of a corresponding one of the firstto third balls 33A to 33C. FIG. 7A is a schematic cross-sectional viewof relevant parts including the support member 31 and the retainingmember 35 having the grooves 32 and 36.

In the state where the retaining member 35 is urged against the supportmember 31 by the urging members, the first ball 33A fits into the firstand fourth grooves 32A and 36A, with about ⅓ of the first ball 33A onone side being inside one of the depressions of the first groove 32A andabout ⅓ of the first ball 33A on the other side being inside one of thedepressions of the fourth groove 36A; the second ball 33B fits into thesecond and fifth grooves 32B and 36B, with about ⅓ of the second ball33B on one side being inside one of the depressions of the second groove32B and about ⅓ of the second ball 33B on the other side being insideone of the depressions of the fifth groove 36B; and the third ball 33Cfits into the third and sixth grooves 32C and 36C, with about ⅓ of thethird ball 33C on one side being inside one of the depressions of thethird groove 32C and about ⅓ of the third ball 33C on the other sidebeing inside one of the depressions of the sixth groove 36C.

In the state where the retaining member 35 is not urged against thesupport member 31, the first ball 33A is movable from one of thedepressions of the first groove 32A to another adjacent thereto over theelevation therebetween, and from one of the depressions of the fourthgroove 36A to another adjacent thereto over the elevation therebetween;the second ball 33B is movable from one of the depressions of the secondgroove 32B to another adjacent thereto over the elevation therebetween,and from one of the depressions of the fifth groove 36B to anotheradjacent thereto over the elevation therebetween; and the third ball 33Cis movable from one of the depressions of the third groove 32C toanother adjacent thereto over the elevation therebetween, and from oneof the depressions of the sixth groove 36C to another adjacent theretoover the elevation therebetween.

The first to third balls 33A to 33C are steel balls for use as ballbearings. The support member 31, the retaining member 35, the urgingplate 37, and the guide member 34 are made of aluminum, POM, aluminum,and ABS, respectively.

The wearing device 20 forms a frame of a pair of glasses. The wearingdevice (frame) 20 includes a front member 21 to be positioned in frontof the observer and two temples 23 turnably attached to respective endsof the front member 21 with hinges (not shown). The attachment members30 are attached to the respective ends of the front member 21(specifically, to the respective securing members 25 provided on thewearing device 20). The front member 21 is provided with a nose pad (notshown) at the center thereof. That is, the wearing device (frame) 20 hassubstantially the same configuration as a pair of normal glasses, exceptthat the wearing device (frame) 20 includes no rims. The frame is madeof any of or any combination of materials such as metal, alloy, andplastic, which are also used for making normal glasses. The wearingdevice 20 is also provided with headphones 24.

When the wearing device 20 is worn on the head of an observer, thedistance (in the first direction) between the right and left imagedisplay devices 100 and the vertical positions (in the second direction)of the right and left image display devices 100 relative to therespective eyes of the observer are adjusted. This adjustment is done byloosening the urging screws 39, so that the retaining members 35 arereleased from the urging force against the support members 31. In thisstate, the support member 31 is moved in the first direction relative tothe retaining member 35. Then, referring to FIG. 7C, the first to thirdballs 33A to 33C each move from one depression in the corresponding oneof the fourth to sixth grooves 36A to 36C to another adjacent theretoover the elevation therebetween. Thus, the distance (in the firstdirection) between the right and left image display devices 100 can beadjusted. Furthermore, the support member 31 is moved in the seconddirection relative to the retaining member 35. Then, the first to thirdballs 33A to 33C each move from one depression in the corresponding oneof the first to third grooves 32A to 32C to another adjacent theretoover the elevation therebetween. Thus, the vertical positions (in thesecond direction) of the right and left image display devices 100relative to the respective eyes of the observer can be adjusted.Subsequently, the urging screws 39 are fastened, so that the retainingmember 35 is urged against the support member 31. Thus, play between theretaining member 35 and the support member 31 is eliminated.

As described above, the head-mounted display apparatus of the firstexemplary embodiment includes the attachment members 30 with which theimage display devices 100 are attached to the wearing device 20. Theattachment members 30 are each capable of adjusting the position of thecorresponding image display device 100 relative to the wearing device 20independently in the first and second directions. Thus, the overallconfiguration of the head-mounted display apparatus can be simplified,making it easier to realize a design with a reduced number of componentsto be positioned in front of the observer's face. Furthermore, theoverall size and weight of the head-mounted display apparatus can bereduced.

FIG. 8 is a conceptual diagram of one of the image display devices 100included in the head-mounted display apparatus of the first exemplaryembodiment. The image display device 100 included in the head-mounteddisplay apparatus of the first exemplary embodiment includes an imagegenerator having the first configuration and an optical device havingthe first configuration.

The image display device 100 includes the following:

(A-1) an image generator 110 having the first configuration; and

(A-2) an optical device (light-guiding means) 120 receiving light fromthe image generator 110, guiding the light, and outputting the lighttoward an eye 41 of an observer.

The optical device 120 is attached to the image generator 110.

In the first exemplary embodiment shown in FIG. 8, the optical device120 has the first configuration including the following:

(A-2-1) a light-guiding plate 121 causing the light received from theimage generator 110 to propagate with total reflection thereinsidebefore outputting the light toward the eye 41 of the observer;

(A-2-2) a first deflector 130 deflecting the light received by thelight-guiding plate 121 so that the light is totally reflected insidethe light-guiding plate 121; and

(A-2-3) a second deflector 140 deflecting, a plurality of times, thelight caused to propagate with total reflection inside the light-guidingplate 121 so that the light is output from the light-guiding plate 121.

The first and second deflectors 130 and 140 are provided inside thelight-guiding plate 121. The first deflector 130 reflects the lightreceived by the light-guiding plate 121. The second deflector 140transmits and reflects, a plurality of times, the light caused topropagate with total reflection inside the light-guiding plate 121. Thatis, the first deflector 130 functions as a reflective mirror, whereasthe second deflector 140 functions as a transflective mirror.Specifically, the first deflector 130 provided inside the light-guidingplate 121 is made of aluminum and includes a light-reflecting film (akind of mirror) reflecting the light received by the light-guiding plate121. Whereas, the second deflector 140 provided inside the light-guidingplate 121 is a multilayer structure in which a number of dielectricfilms are stacked. The dielectric films include, for example, TiO2 filmshaving high dielectric constants and SiO2 films having low dielectricconstants. An exemplary multilayer structure in which a number ofdielectric films are stacked is disclosed in Japanese Unexamined PatentApplication Publication (Translation of PCT Application) No.2005-521099. Although FIG. 8 shows a structure including six dielectricfilms, the multilayer structure is not limited thereto. Thin pieces madeof the same material as of the light-guiding plate 121 are providedbetween the dielectric films. At the first deflector 130, the parallellight received by the light-guiding plate 121 is reflected (ordiffracted) in such a manner as to be totally reflected inside thelight-guiding plate 121. At the second deflector 140, the parallel lightcaused to propagate with total reflection inside the light-guiding plate121 is reflected (or diffracted) a plurality of times and issubsequently output, maintaining the form of parallel light, from thelight-guiding plate 121.

The first deflector 130 can be obtained in the following manner. Aportion 124 of the light-guiding plate 121 defined by a plane in whichthe first deflector 130 is to be provided is cut off, whereby a slantingsurface on which the first deflector 130 is to be provided is formed.Then, after a light-reflecting film is formed on the slanting surface byvacuum deposition, the portion 124 is bonded back onto the resultingfirst deflector 130. The second deflector 140 can be obtained in thefollowing manner. First, a multilayer structure in which thin piecesmade of the same material as of the light-guiding plate 121 (glass, forexample) and dielectric films (obtained by vacuum deposition, forexample) are alternately stacked is manufactured. A portion 125 of thelight-guiding plate 121 defined by a plane in which the second deflector140 is to be provided is cut off, whereby a slanting surface is formed.Then, after the multilayer structure is bonded onto the slantingsurface, the outer shape of the resulting structure is adjusted bypolishing or the like. Thus, the optical device 120 can be obtained inwhich the first deflector 130 and the second deflector 140 areincorporated in the light-guiding plate 121.

The light-guiding plate 121, made of optical glass or plastic material,has two parallel surfaces (a first surface 122 and a second surface 123)extending parallel to the axis of the light-guiding plate 121. The firstsurface 122 and the second surface 123 are positioned opposite eachother. The parallel light enters from a portion, forming a plane ofincidence, of the first surface 122, propagates with total reflectioninside the light-guiding plate 121, and emerges from another portion,forming a plane of emergence, of the first surface 122.

Referring to FIG. 8, the image generator 110 having the firstconfiguration includes the following:

(A-1-1) an image-forming device 111 having a plurality of pixelsarranged in a two-dimensional matrix; and

(A-1-2) a collimating optical system 112 collimating the light from thepixels of the image-forming device 111 into parallel light andoutputting the parallel light.

The image generator 110 is covered with the cover 113.

The image-forming device 111 includes a reflective spatial-lightmodulator 150 and a light source 153. The light source 153 includes alight-emitting diode that emits white light. Specifically, thereflective spatial-light modulator 150 includes a liquid crystal display(LCD) device 151 that is an LCOS serving as a light valve, and apolarization beam splitter 152 that reflects part of light from thelight source 153 and guides the part of light to the LCD device 151while allowing part of the light reflected by the LCD device 151 to passtherethrough and guiding the part of the light to the collimatingoptical system 112. The LCD device 151 has a plurality (320×240, forexample) of pixels arranged in a two-dimensional matrix. Thepolarization beam splitter 152 has the same configuration as in therelated art. The light emitted as unpolarized light from the lightsource 153 strikes the polarization beam splitter 152. The polarizationbeam splitter 152 allows p-polarized components to pass therethrough soas to be output to the outside of its system, whereas the polarizationbeam splitter 152 reflects s-polarized components. The reflecteds-polarized components enter the LCD device 151, are reflectedthereinside, and are output to the outside. Among the light that isoutput from the LCD device 151, light that is output from pixelsdisplaying “white” contain a relatively large number of p-polarizedcomponents, and light that is output from pixels displaying “black”contain a relatively large number of s-polarized components. That is,among the light that strikes the polarization beam splitter 152 afterbeing output from the LCD device 151, p-polarized components passthrough the polarization beam splitter 152 and are guided toward thecollimating optical system 112, whereas s-polarized components arereflected by the polarization beam splitter 152 and are fed back to thelight source 153. The LCD device 151 includes the plurality of pixels(320×240 pixels, for example, with the number of liquid crystal cellsbeing three times larger than the number of pixels) that are arrangedin, for example, a two-dimensional matrix. The collimating opticalsystem 112 is a convex lens, for example. The image-forming device 111(specifically, the LCD device 151) is positioned at a distance from thecollimating optical system 112 corresponding to the focal length of thecollimating optical system 112 so that parallel light is produced. Eachof the pixels includes a red-light-emitting subpixel that emits redlight, a green-light-emitting subpixel that emits green light, and ablue-light-emitting subpixel that emits blue light.

A second exemplary embodiment is a variation of the first exemplaryembodiment. FIG. 9 is a conceptual diagram of one of image displaydevices 200 included in a head-mounted display apparatus of the secondexemplary embodiment. The image display device 200 of the secondexemplary embodiment includes an image generator 210 having the secondconfiguration. Specifically, the image generator 210 includes thefollowing:

(A-1-1) a light source 251;

(A-1-2) a collimating optical system 252 collimating light from thelight source 251 into parallel light;

(A-1-3) a scanner 253 scanningly moving the parallel light from thecollimating optical system 252; and

(A-1-4) a relay optical system 254 relaying and outputting the parallellight scanningly moved by the scanner 253.

The image generator 210 is covered with a cover 213.

The light source 251 includes a red-light-emitting element 251R thatemits red light, a green-light-emitting element 251G that emits greenlight, and a blue-light-emitting element 251B that emits blue light. Thelight-emitting elements 251R, 251G, and 251B are semiconductor laserelements. Rays of light of the three primary colors emitted from thelight source 251 are transmitted through a cross prism 255, therebybeing combined into a single ray of light. The light enters and iscollimated by the collimating optical system 252, which has a positiveoptical power on the whole, and is output therefrom as parallel light.The parallel light is reflected by a total-reflection mirror 256, and isscanningly moved by the scanner 253 in the horizontal and verticaldirections. The scanner 253 is a MEMS and includes a micromirrorrotatable in two-dimensional directions so that the parallel lightreceived thereat is scanningly moved in two-dimensional directions. Theparallel light scanningly moved in such a manner is imaged twodimensionally, whereby virtual pixels are generated. Light from thevirtual pixels is transmitted through the relay optical system 254,which is a related-art relay optical system, thereby becoming parallellight, and the parallel light enters the optical device 120.

The optical device 120 that receives, guides, and outputs the parallellight from the relay optical system 254 has the same configuration asthe optical device 120 of the first exemplary embodiment, and detaileddescription thereof is therefore omitted. The head-mounted displayapparatus of the second exemplary embodiment also has substantially thesame configuration as in the first exemplary embodiment except for theimage generator 210, as described above, and detailed descriptionthereof is therefore omitted.

A third exemplary embodiment is another variation of the first exemplaryembodiment. FIG. 10A is a conceptual diagram of one of image displaydevices 300 included in a head-mounted display apparatus according tothe third exemplary embodiment. FIG. 10B is a schematic enlargedcross-sectional view showing a part of a reflective volume-hologramdiffraction grating. The third exemplary embodiment employs the imagegenerator 110 having the first configuration, as in the first exemplaryembodiment, and an optical device (light-guiding means) 320 basicallyhaving the same configuration as the optical device 120 of the firstexemplary embodiment, except for the configurations of the firstdeflector and the second deflector. The optical device 320 includes thefollowing:

(A-2-1) a light-guiding plate 321 causing the light received from theimage generator 110 to propagate with total reflection thereinsidebefore outputting the light toward the eye 41 of the observer;

(A-2-2) a first deflector 330 deflecting the light received by thelight-guiding plate 321 so that the light is totally reflected insidethe light-guiding plate 321; and

(A-2-3) a second deflector 340 deflecting, a plurality of times, thelight caused to propagate with total reflection inside the light-guidingplate 321 so that the light is output from the light-guiding plate 321.

The optical device 320 of the third exemplary embodiment has the secondconfiguration. Specifically, the first deflector and the seconddeflector are provided on a surface of the light-guiding plate 321 (morespecifically, a second surface 323 of the light-guiding plate 321). Thefirst deflector diffracts the light received by the light-guiding plate321, and the second deflector diffracts, a plurality of times, the lightcaused to propagate with total reflection inside the light-guiding plate321. In this case, the first and second deflectors are diffractiongrating elements, specifically, reflective diffraction grating elements,more specifically, reflective volume-hologram diffraction gratings. Forconvenience of description hereinafter, a first deflector constituted bya reflective volume-hologram diffraction grating will be referred to asa “first diffraction grating member 330”, and a second deflectorconstituted by a reflective volume-hologram diffraction grating will bereferred to as a “second diffraction grating member 340”.

In the third exemplary embodiment and in a fourth exemplary embodimentdescribed below, to accommodate diffraction reflections of a number P(specifically, P=3, corresponding to three colors of red, green, andblue) of kinds of light having a number P of different spectrum bands(or wavelengths), the first and second diffraction grating members 330and 340 each include a number P of diffraction grating layers, asreflective volume-hologram diffraction gratings, that are stacked one ontop of another. The diffraction grating layers are made of photopolymermaterial and each have a single pattern of interference fringescorresponding to one of the spectrum bands (or wavelengths). Thediffraction grating layers are manufactured by a related-art method.Specifically, the first and second diffraction grating members 330 and340 each have a structure in which a diffraction grating layer thatdiffracts and reflects red light, a diffraction grating layer thatdiffracts and reflects green light, and a diffraction grating layer thatdiffracts and reflects blue light are stacked. The interference fringesprovided in the diffraction grating layers (diffraction opticalelements) are arranged at a constant pitch and extend linearly in theZ-axis direction, where the axial direction of the first and seconddiffraction grating members 330 and 340 is defined as the Y-axisdirection, and the direction of the normal to the first and seconddiffraction grating members 330 and 340 is defined as the X-axisdirection. In FIGS. 10A and 11, the first and second diffraction gratingmembers 330 and 340 are each shown as a single layer. With theconfiguration described above, light of the different spectrum bands (orwavelengths) can be diffracted and reflected by the first and seconddiffraction grating members 330 and 340 with an increased diffractionefficiency, a widened diffraction acceptance angle, and an optimizeddiffraction angle.

FIG. 10B is a schematic enlarged cross-sectional view showing a part ofthe reflective volume-hologram diffraction grating. The reflectivevolume-hologram diffraction grating has interference fringes provided ata slant angle φ. The slant angle φ is an angle formed between thesurface of the reflective volume-hologram diffraction grating and eachof the interference fringes. The interference fringes extend inside thereflective volume-hologram diffraction grating, from one surface thereofto the other, and satisfies the Bragg conditions. Under the Braggconditions, the following expression is satisfied:

m·λ=2·d·sin(Θ)  (A)

where m denotes a positive integer, λ denotes the wavelength, d denotesthe pitch between grating planes (the interval between virtual planescontaining the interference fringes in the direction of the normalthereto), and Θ denotes the supplementary angle with respect to theincidence angle at the interference fringe.

In a case where light is incident on the diffraction grating member atan incident angle ψ, the relationship between the supplementary angle Θ,the slant angle φ, and the incidence angle ψ is expressed as follows:

Θ=90°−(φ+ψ)  (B)

The first diffraction grating member 330, provided (bonded) on thesecond surface 323 of the light-guiding plate 321 as described above,diffracts and reflects the parallel light entering the light-guidingplate 321 through a first surface 322 of the light-guiding plate 321 sothat the parallel light is totally reflected inside the light-guidingplate 321. The second diffraction grating member 340, provided (bonded)on the second surface 323 of the light-guiding plate 321 as describedabove, diffracts and reflects, a plurality of times, the parallel lightcaused to propagate with total reflection inside the light-guiding plate321, and outputs the light, maintaining the form of parallel light, fromthe light-guiding plate 321 through the first surface 322.

Also in the light-guiding plate 321, parallel light having three colorsof red, green and blue propagates with total reflection inside thelight-guiding plate 321 and is subsequently output. Since the lightguided by the light-guiding plate 321 travels inside the light-guidingplate 321 along a long optical path, the number of total reflectionsoccurring before the light reaches the second diffraction grating member340 varies with the angle of view. Specifically, among parallel raysthat enter the light-guiding plate 321, some rays that enter thelight-guiding plate 321 at angles toward the second diffraction gratingmember 340 cause less reflections than other rays that enter thelight-guiding plate 321 at angles away from the second diffractiongrating member 340. This is because, among the parallel rays that arediffracted and reflected by the first diffraction grating member 330,rays that enter the light-guiding plate 321 at angles toward the seconddiffraction grating member 340 form smaller angles with respect to thenormal to the light-guiding plate 321 when striking the inner surfacesof the light-guiding plate 321 while propagating inside thelight-guiding plate 321, than rays that enter the light-guiding plate321 at angles away from the second diffraction grating member 340. Inaddition, the pattern of the interference fringes provided inside thesecond diffraction grating member 340 and the pattern of theinterference fringes provided inside the first diffraction gratingmember 330 are symmetrical with respect to a virtual plane perpendicularto the axis of the light-guiding plate 321.

The fourth exemplary embodiment described below also employs thelight-guiding plate 321 basically having the same configuration as thelight-guiding plate 321 in the third exemplary embodiment.

The head-mounted display apparatus of the third exemplary embodiment hassubstantially the same configuration as in the first exemplaryembodiment except for the optical device 320, as described above, anddetailed description thereof is therefore omitted.

A fourth exemplary embodiment is a variation of the third exemplaryembodiment. FIG. 11 is a conceptual diagram of one of image displaydevices 400 included in a head-mounted display apparatus according tothe fourth exemplary embodiment. The image display device 400 of thefourth exemplary embodiment includes the light source 251, thecollimating optical system 252, the scanner 253, the relay opticalsystem 254, and so forth, having the same configurations as in thesecond exemplary embodiment. The fourth exemplary embodiment employs theoptical device 320, the same configuration as in the third exemplaryembodiment. Except for the foregoing points, the head-mounted displayapparatus of the fourth exemplary embodiment has substantially the sameconfiguration as in the first exemplary embodiment, and detaileddescription thereof is therefore omitted.

A fifth exemplary embodiment is another variation of the first exemplaryembodiment. FIG. 12 is a conceptual diagram of one of image displaydevices included in a head-mounted display apparatus according to thefifth exemplary embodiment. The fifth exemplary embodiment employs anoptical device having the third configuration. Specifically, the opticaldevice includes a transflective mirror 520 receiving light from theimage generator 110 and outputting the light toward the eye 41 of theobserver. In the fifth exemplary embodiment, the light output from theimage generator 110 propagates inside a transparent member 521, such asa glass plate or a plastic plate, and enters the transflective mirror520. Alternatively, the light output from the image generator 110 maypropagate in the air before entering the transflective mirror 520. Inaddition, the image generator 110 may be replaced with the imagegenerator 210 described in the second exemplary embodiment. Except forthe foregoing points, the head-mounted display apparatus of the fifthexemplary embodiment has substantially the same configuration as in thefirst exemplary embodiment, and detailed description thereof istherefore omitted.

While the present application has been described with reference topreferred embodiments, the present application is not limited thereto.The head-mounted display apparatuses, the image display devices, thewearing devices, the attachment members, the support members, theretaining members, and the urging members described in the aboveembodiments are only exemplary and can be changed appropriately. Forexample, the number of grooves provided in the support member, thenumber of grooves provided in the retaining member, and the number ofballs may alternatively be four or more. Surface-relief hologram gratingmembers (refer to U.S. Patent No. 20040062505 A1) may alternatively beprovided on the light-guiding plate. In the third and fourth exemplaryembodiment, the optical device 320 may alternatively includetransmissive diffraction grating elements, or a reflective diffractiongrating element for one of the first and second deflectors and atransmissive diffraction grating element for the other. As anotheralternative, the diffraction grating elements may be reflective blazeddiffraction grating elements.

FIG. 13 is a conceptual diagram of an active-matrix image-forming devicesuitable for use as a variation of each of the image-forming devices inthe first, third, and fifth exemplary embodiments. The active-matriximage-forming device includes a light-emitting panel on whichlight-emitting elements 601, which are semiconductor light-emittingelements, are arranged in a two-dimensional matrix. An image isdisplayed by controlling the light-emitting elements 601 to individuallyswitch between emitting and non-emitting states so that the states ofemission of the light-emitting elements 601 are directly observed. Lightemitted from the image-forming device travels through the collimatingoptical system 112 and enters the light-guiding plate 121 or 321.

Alternatively, referring to a conceptual diagram shown in FIG. 14, theremay be employed an image-forming device including the following:

(α) a red-light-emitting panel 611R on which red-light-emitting elements601R that emit red light are arranged in a two-dimensional matrix;

(β) a green-light-emitting panel 611G on which green-light-emittingelements 601G that emit green light are arranged in a two-dimensionalmatrix;

(γ) a blue-light-emitting panel 611B on which blue-light-emittingelements 601B that emit blue light are arranged in a two-dimensionalmatrix; and

(δ) means (for example, a dichroic prism 603) for combining lightemitted from the red-, green-, and blue-light-emitting panels 611R,611G, and 611B into a single ray of light.

The image-forming device displays a color image by controlling the red-,green-, and blue-light-emitting elements 601R, 601G, and 601B toindividually switch between emitting and non-emitting states. Lightemitted from this image-forming device also travels through thecollimating optical system 112 and enters the light-guiding plate 121 or321. The image-forming device also includes microlenses 612 thatcondenses light emitted from the light-emitting elements 601R, 601G, and601B.

FIG. 15 is a conceptual diagram of another alternative image-formingdevice including the light-emitting panels 611R, 611G, and 611B on whichthe light-emitting elements 601R, 601G, and 601B are arranged intwo-dimensional matrices, respectively. Light emitted from thelight-emitting panels 611R, 611G, and 611B is controlled bylight-passage control devices 604R, 604G, and 604B to pass therethroughor to be blocked thereby. The light that has passed through thelight-passage control devices 604R, 604G, and 604B enters the dichroicprism 603, thereby being combined into a single ray of light. The lightfurther travels through the collimating optical system 112, and entersthe light-guiding plate 121 or 321.

FIG. 16 is a conceptual diagram of another alternative image-formingdevice including the light-emitting panels 611R, 611G, and 611B on whichthe light-emitting elements 601R, 601G, and 601B are arranged intwo-dimensional matrices, respectively. Light emitted from thelight-emitting panels 611R, 611G, and 611B enters the dichroic prism603, thereby being combined into a single ray of light. The light outputfrom the dichroic prism 603 is controlled by a light-passage controldevice 604 to pass therethrough or to be blocked thereby. The light thathas passed through the light-passage control device 604 further travelsthrough the collimating optical system 112, and enters the light-guidingplate 121 or 321.

FIG. 17 shows another alternative image-forming device. Theimage-forming device includes a light-emitting element 601R that emitsred light; a light-passage control device (for example, a liquid crystaldisplay device 604R), which is a kind of a light valve that controls thelight emitted from the light-emitting element 601R to pass therethroughor to be blocked thereby; a light-emitting element 601G that emits greenlight; a light-passage control device (for example, a liquid crystaldisplay device 604G), which is a kind of a light valve that controls thelight emitted from the light-emitting element 601G to pass therethroughor to be blocked thereby; a light-emitting element 601B that emits bluelight; a light-passage control device (for example, a liquid crystaldisplay device 604B), which is a kind of a light valve that controls thelight emitted from the light-emitting element 601B to pass therethroughor to be blocked thereby; light-guiding members 602 that guide the lightemitted from the respective light-emitting elements 601R, 601G, and601B, which are GaN-based semiconductor elements; and means (forexample, the dichroic prism 603) for combining the light from thelight-emitting elements 601R, 601G, and 601B into a single ray of light.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A head-mounted display apparatuscomprising: an image display device; a wearing device with which theimage display device is worn on a head of an observer; and an attachmentmember with which the image display device is attached to the wearingdevice, wherein the attachment member is capable of adjusting a positionof the image display device relative to the wearing device independentlyin a first direction and in a second direction, the first directionbeing defined by a virtual line connecting centers of eyes of theobserver, the second direction being perpendicular to the firstdirection and extending vertically with respect to the observer.
 2. Thehead-mounted display apparatus according to claim 1, wherein the imagedisplay device and the attachment member are provided for each of rightand left eyes.
 3. The head-mounted display apparatus according to claim1, wherein the image display device includes an image generator; and anoptical device receiving light from the image generator, guiding thelight, and outputting the light toward a corresponding one of the eyesof the observer.
 4. The head-mounted display apparatus according toclaim 3, wherein the optical device includes a light-guiding platecausing the received light to propagate with total reflectionthereinside before outputting the light; first deflecting meansdeflecting the light received by the light-guiding plate so that thelight is totally reflected inside the light-guiding plate; and seconddeflecting means deflecting, a plurality of times, the light caused topropagate with total reflection inside the light-guiding plate so thatthe light is output from the light-guiding plate.
 5. The head-mounteddisplay apparatus according to claim 4, wherein the first deflectingmeans reflects the light received by the light-guiding plate, andwherein the second deflecting means transmits and reflects, a pluralityof times, the light caused to propagate with total reflection inside thelight-guiding plate.
 6. The head-mounted display apparatus according toclaim 5, wherein the first deflecting means functions as a reflectivemirror, and wherein the second deflecting means functions as atransflective mirror.
 7. The head-mounted display apparatus according toclaim 4, wherein the first deflecting means diffracts the light receivedby the light-guiding plate, and wherein the second deflecting meansdiffracts, a plurality of times, the light caused to propagate withtotal reflection inside the light-guiding plate.
 8. The head-mounteddisplay apparatus according to claim 7, wherein the first and seconddeflecting means include diffraction grating elements.
 9. Thehead-mounted display apparatus according to claim 8, wherein thediffraction grating elements are reflective diffraction gratingelements.
 10. The head-mounted display apparatus according to claim 8,wherein the diffraction grating elements are transmissive diffractiongrating elements.
 11. The head-mounted display apparatus according toclaim 8, wherein one of the diffraction grating elements is a reflectivediffraction grating element and the other is a transmissive diffractiongrating element.
 12. The head-mounted display apparatus according toclaim 3, wherein the optical device includes a transflective mirrorreceiving the light from the image generator and outputting the lighttoward the eye of the observer.
 13. The head-mounted display apparatusaccording to claim 3, wherein the image generator includes animage-forming device having a plurality of pixels arranged in atwo-dimensional matrix; and a collimating optical system collimating thelight from the pixels of the image-forming device into parallel lightand outputting the parallel light.
 14. The head-mounted displayapparatus according to claim 3, wherein the image generator includes alight source; a collimating optical system collimating light from thelight source into parallel light; scanning means scanningly moving theparallel light from the collimating optical system; and a relay opticalsystem relaying and outputting the parallel light scanningly moved bythe scanning means.
 15. The head-mounted display apparatus according toclaim 1, wherein the wearing device forms a frame of a pair of glasses.16. The head-mounted display apparatus according to claim 15, whereinthe frame includes a front member to be positioned in front of theobserver; and two temples turnably attached to respective ends of thefront member with hinges, and wherein the attachment member is attachedto each of the ends of the front member.